1. Field of the Invention
The present invention relates to the field of control systems for engines, and in particular to control systems for optimizing engine performance.
2. Prior Art
One type of engine control system is the ignition system, which provides a timed spark for igniting the fuel and air mixture. The performance of the engine is highly dependent upon the precise instant at which the spark is delivered to the combustion chamber. Thus, even though in the typical engine, the throttle is the primary control for varying the engine speed, if the spark is not delivered at the appropriate instant, the engine speed for that throttle setting will not be optimized.
The most common ignition system for internal combustion engines is that generally known as the Kettering ignition system. The Kettering system comprises generally a primary, low voltage circuit, and a secondary, high voltage circuit. The primary circuit includes the battery, distributor cam-operated breaker points and the heavy primary windings of the ignition coil. The secondary circuit includes the secondary windings of the ignition coil, the distributor rotor, cap, ignition cables and spark plugs. When the breaker points are closed, the primary circuit is completed through ground, allowing current to flow in the primary circuit through the primary windings, building a magnetic field in the coil. As the engine rotates, the cam within the distributor housing is turned, pushing against the rubbing block of the points and forcing the breaker points apart. Separation of the breaker points interrupts the primary circuit and stops the primary current flow. When the current flow stops, the magnetic field in the coil collapses through the secondary windings. Field collapse induces a momentary high voltage surge in the secondary windings. At this instant the rotor tip is lined up with the proper distributor cap electrode. The high voltage surge is impressed through the ignition cable to the spark plug, causing an arc to form across the spark plug gap to ignite the fuel mixture.
Various improvements have been made to the Kettering system to increase the voltage available to the spark plug, improve reliability and reduce maintenance. One such improvement is the "transistorized" ignition, wherein the breaker points serve only to switch on and off a power transistor, through which the primary current flows. The current flow through the points is greatly reduced, increasing point longevity, and primary current can be increased, thereby increasing the resultant secondary high voltage.
Another popular type of ignition system is the capacitive discharge ignition. This system utilizes a capacitor as the primary energy source. An inverter is typically used to step up the battery voltage and charge the capacitor. An electronic switching element is then used to discharge the capacitor into the primary windings of the ignition coil, inducing a high voltage impulse at the secondary windings and a high voltage pulse at the spark plugs.
Regardless of the system used, the spark must be delivered to the spark plug at the right instant to optimize engine performance. In the conventional automotive ignition system, the timing of the ignition spark is controlled by rotating the distributor housing a few degrees in the required direction to either retard or advance the spark timing. The breaker points are coupled to the housing, and rotate with it. When the desired spark timing is achieved, the housing is secured in position. Modern ignition systems utilize centrifugal mechanical advance mechanisms and vacuum timing advance mechanisms to change ignition timing to compensate for throttle position and engine load. These mechanisms, however, are relatively crude devices, pre-adjusted at the automotive factory and typically not adjusted unless a perceptible problem develops. Moreover, the timing advance curve is selected for a given engine or vehicle model, and is used for many vehicles; no fine-tuning is utilized to peak the engine speed and efficiency. As the engine wears and the ignition system deteriorates, the timing may also change, requiring frequent ignition tune-ups to maintain performance at an acceptable level.
Some modern automobile engines are fitted with minicomputers which receive inputs from a plurality of sensors monitoring factors such as engine RPM, manifold vacuum, engine temperature, and exhaust emissions content, and adjusting the spark timing to a preset value based upon such factors. Such systems are expensive, requiring complex circuitry and a plurality of sensors, suffer from reliability problems, and still do not adjust the timing to that value which optimizes performance necessarily, but rather to a preset value not based solely upon engine performance.